From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Re: [PATCH] cgroup: fix to allow mounting a hierarchy by name
Date: Thu, 5 Jan 2012 18:27:34 -0800
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To: Li Zefan <lizf-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
Cc: LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>

Hello,

On Fri, Jan 06, 2012 at 10:24:47AM +0800, Li Zefan wrote:
> There's a corner case where "mount --bind" can't be used:
> 
> 	# mount -t cgroup -o none,name=hier1 xxx /mnt
> 	# mkdir /mnt/tmp
> 	# umount /mnt
> 
> Since there's a sub-cgroup in it, umount won't destroy the hierarchy,
> but "hide" it, so the name=xxx is necessary to re-mount it.
>
> > Also, what's the use case for
> > mounting the same cgroup directory multiple times?  Why is that
> > necessary?  Is it useful for some namespace-savvy setup?
> 
> I don't have a use case in real life. It was made so at the very
> beginning of cgroup, and we should't break it without strong reasons.
> We can mount other pseudo filesystems like procfs, sysfs and debugfs
> multiple times, right?

Yeah, we shouldn't break it so I applied the patch with a lot of
grumbling.  This is something which shouldn't have existed at all. :(

Thanks a lot for the explanation and patience.

-- 
tejun